1. Field of the Invention
The present invention relates to a driving mechanism for a large multi-piece rim for a wheel of an industrial vehicle and, in particular, to a driving mechanism using a driver loose-key between the rim base and the bead seat band of a multi-piece rim wherein the bead seat band, a pair of side rings and a lock ring are provided about the periphery of the rim base.
2. Description of the Prior Art
Multi-piece rims, which include a rim base, a bead seat band attached about the periphery of the rim base via an O ring and holding a bead portion of a tire from a radially inner side thereof, a pair of side rings each holding a bead portion of the tire from an axially outer side thereof, and a lock ring provided between the rim base and the bead seat band for locking the bead seat band on the rim base, are well known. In a large multi-piece rim used for a wheel of an industrial vehicle such as a construction vehicle, a driving mechanism having a driver-loose key is provided between the rim base and the bead seat band in order to minimize circumferential slippage of the bead seat band on the rim base.
A conventional driving mechanism is constructed, for example, as shown in FIGS. 5 and 6. Multi-piece rim 1 has rim base 2, bead seat band 4 attached about the periphery of the rim base via lock ring 6, side ring 5 provided about the periphery of the bead seat band and an O ring 3 provided between the rim base and the bead seat band. Driving mechanism 7 is constructed of driver pocket 8 fixed on rim base 2, driver pocket 9 fixed on bead seat band 4 and driver-loose key 10 which is cross-shaped. Portions 10a, 10b, 10c and 10d of driver-loose key 10 are inserted into a hole 11 defined in driver pocket 8, a groove 12 defined between driver pockets 9a and 9b, a groove 13a defined between driver pocket 8 and driver pocket 9a and a groove 13b defined between driver pocket 8 and driver pocket 9b, respectively. Portion 10a of driver-loose key 10 engages driver pocket 8 and portion 10b engages driver pocket 9a and/or driver pocket 9b, thereby preventing bead seat band 4 from circumferentially slipping on rim base 2. Driver-loose key 10 is placed at a desirable position in a radial direction of the rim and the driver-loose key is prevented from inclining, by inserting portions 10c and 10d into grooves 13a and 13b respectively. The grooves 13a and 13b are usually arc-shaped in a circumferential direction of the multi-piece rim as shown in FIG. 5, while the portions 10c and 10d of driver-loose key 10 are straight and extend perpendicularly to portions 10a and 10b as shown in FIG. 5 or as also shown in FIG. 1 of U.S. Pat. No. 3,599,697.
In such a conventional driving mechanism, however, since grooves 13a and 13b are arc-shaped having a certain curvature while portions 10c and 10d of driver-loose key 10 are straight, a clearance C.sub.1 (FIG. 5) between portion 10c and an inner surface of groove 13a or between portion 10d and an inner surface of groove 13b must be fairly large, for example, more than 2.5 mm, in order to enable the portion 10c or 10d be inserted into groove 13a or 13b. This large clearance may cause driver-loose key 10 to have a large play. Further the looseness between driver-loose key 10 and driver pocket 8 or 9 tends to increase during use of the multi-piece rim 1 if the clearance C.sub.1 is large. If the looseness increases, inclination of driver-loose key 10 will occur as shown in FIG. 7. In such a state, a fairly great slippage S.sub.1 of bead seat band 4 on rim base 2 is allowed, thereby decreasing the ability of the driving mechanism to control slippage. If the amount of slippage S.sub.1 becomes too great, O ring 3 is distorted or abraded and air can then leak from inside the tire.
Moreover, since the contact area between the arcuate inner surfaces of grooves 13a and 13b and the straight portions 10c and 10d of driver-loose key 10 is a point contact or at best a line contact, large local loads are applied to the tip portions of portions 10c and 10d or the inner surfaces of grooves 13a and 13b when a load in the circumferential direction is transmitted via driver-loose key 10. The large local loads will cause abrasion or deformation of these portions, thereby decreasing the durability of the driving mechanism.